fractional selectivity

in catalysis
https://doi.org/10.1351/goldbook.F02496
The term
selectivity
(S) is used to describe the relative rates of two or more competing reactions on a
catalyst
. Such
competition
includes cases of different reactants undergoing
simultaneous reactions
or of a single reactant taking part in two or more reactions. For the latter case, S may be defined in two ways. The first of these defines a fractional
selectivity
, SF, for each product by the equation SF=ξiξi The second defines relative selectivities, SR, for each pair of products by SR=ξiξj In each case, ξi and ξj are the rates of increase of the
extent of reactions
i and j respectively, i.e. ξi=dξidt and ξj=dξjdt where ξi and ξj are the extents of reactions i and j respectively.
Source:
PAC, 1976, 46, 71. (Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix II. Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Part II: Heterogeneous Catalysis) on page 81 [Terms] [Paper]